1. Field of the Invention
The present invention relates to piezoelectric devices, in particular, to a piezoelectric device, such as a piezoelectric actuator, including a piezoelectric ceramic containing a perovskite complex oxide as a main component and electrodes containing copper as a main component.
2. Description of the Related Art
Piezoelectric actuators that utilize electrostrictive effects generated by the application of voltage to piezoelectric ceramics are commonly used for alignment of precision machine tools and in print heads of ink jet printers.
A piezoelectric device used as such a piezoelectric actuator is typically fabricated by applying, by printing, a conductive paste on ceramic green sheets containing piezoelectric ceramic powder to form conductive layers, stacking a predetermined number of ceramic green sheets with the conductive layers thereon, simultaneously firing the conductive layers and the ceramic green sheets to form a piezoelectric ceramic compact including co-sintered piezoelectric ceramic and internal electrodes, and then forming external electrodes on side surfaces of the piezoelectric ceramic compact.
In this type of piezoelectric device, a noble metal material, such as Ag—Pd alloys, having high melting points and not readily oxidizable in a high-temperature, oxidizing atmosphere has been used as the material for the internal electrodes.
However, the use of noble metal materials as the internal electrode material increases the cost of the material. In this regard, use of base metal materials, such as relatively inexpensive copper and the like, has been suggested recently.
For example, Japanese Unexamined Patent Application Publication No. 2002-255644 discloses a multilayer piezoelectric device including layers of a PZT (lead zirconate titanate, Pb(Ti, Zr) O3) piezoelectric ceramic and layers of internal electrode stacked in an alternating manner.
Japanese Unexamined Patent Application Publication No. 2002-261343 discloses an electromechanical transducer including a PZT piezoelectric ceramic integrated with internal electrodes by firing, in which the internal electrodes are mainly composed of a base metal material, such as copper or a copper alloy, having a rigidity of 160 GPa or less.
PCT Japanese Translation Patent Publication No. 2003-529917 discloses a piezoelectric structural device including a PZT piezoelectric ceramic and electrodes containing copper. A piezoelectric structural device in which the B sites of the PZT piezoelectric ceramic are partly substituted with divalent metal cations acting as acceptors or pentavalent metal cations acting as donors is also disclosed.
The piezoelectric device used as the piezoelectric actuator described above is used as a mechanical driving source and thus is required to have a large displacement. In order to achieve a large displacement within a limited device size, the piezoelectric constant d must be large.